Search engine providers store different indexes of Uniform Resource Locators (URLs). A first index, of a search engine provider, may store a URL for a particular web page. A second index, of the search engine provider, may store a different URL for the same particular web page. The first index may be created due to the activity of a web crawler, while the second index may be created due to submissions of URLs by operators of websites, which include the web page. Some users may access the particular web page via a first search engine that uses the first index. Other users may access the particular web page via a second search engine that uses the second index. As a result, the search engine provider is unable to determine when users are accessing the same particular web page because different users are using different URLs to access the particular web page.